Method and apparatus for processing exhaust gas in internal combustion engine

ABSTRACT

An exhaust gas processing apparatus ( 26 ) has a bypass passage ( 31   a ) arranged in parallel with exhaust turbine ( 24   b ), an actuator ( 33 ) for opening/closing a bypass valve ( 32 ) to open/close the bypass passage, a fuel supplying valve ( 29 ) for supplying fuel to an exhaust passage ( 22   a ) upstream of a branch portion between the exhaust and bypass passages, a glow plug ( 30 ) for igniting the fuel supplied from the fuel valve, and an ECU ( 13 ) including a processing mode selecting unit ( 13   k ) for selecting a first exhaust gas processing mode for igniting the fuel to introduce the ignited fuel from the bypass passage to an exhaust emission purifier ( 25 ), or a second exhaust gas processing mode for introducing the fuel supplied to the exhaust passage through an exhaust turbine ( 24   b ) to the exhaust emission purifier without igniting the fuel, based upon whether or not there is a flame failure of the fuel.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for processing an exhaust gas introduced to an exhaust emission purifier in an internal combustion engine in which an exhaust turbocharger and the exhaust emission purifier are attached.

BACKGROUND ART

In recent years, for complying with strict exhaust gas regulations applied to an internal combustion engine, it is necessary to activate an exhaust emission purifier at the time of starting up the internal combustion engine for securely purifying the exhaust gas even at a warm-up time. Therefore, Patent Literature 1 has proposed an internal combustion engine in which an exhaust gas heating system is incorporated in an exhaust passage upstream of the exhaust emission purifier. The exhaust gas heating system supplies a high-temperature burning gas to the exhaust emission purifier prior to a warm-up of the internal combustion engine to perform activation of the exhaust emission purifier, and thereafter, the internal combustion engine is cranked, thus starting the warm-up thereof. Therefore, the exhaust gas heating system is generally provided with a fuel supplying valve for supplying fuel to the exhaust passage independently from a combustion chamber in the internal combustion engine and an igniting unit such as a glow plug for heating the fuel to be ignited in the exhaust passage, thereby generating a burning gas.

Citation List Patent Literature

PTL 1: Japanese Patent Laid-Open No. 2003-522875

SUMMARY OF INVENTION Technical Problem

The conventional exhaust gas heating system disclosed in Patent Literature 1 functions only in a case where the internal combustion engine is in a stop condition. Therefore, at a cold time of the internal combustion engine, long time is taken from start of a starting operation in the internal combustion engine to actual completion of the warm-up thereof, resulting in much wasteful consumption of the fuel. In addition, it is necessary to incorporate a supply source of secondary air such as a blower for supplying the burning gas to the exhaust emission purifier at a stop time of the internal combustion engine, into an engine room. For incorporating the supply source in the engine room, a relatively large space is required, thus interrupting downsizing of the engine room. In addition, when the exhaust gas heating system is activated during the operating of the internal combustion engine, the flame misses due to a flow speed of the exhaust gas flowing in the exhaust passage. Therefore, the exhaust gas heating system can not be used in a case where the exhaust emission purifier becomes inactive during the operating of the internal combustion engine or for maintaining an active state of the exhaust emission purifier.

An object of the present invention is to provide a method for processing an exhaust gas by which in an internal combustion engine in which an exhaust gas heating system is incorporated in an exhaust passage upstream of an exhaust emission purifier for heating an exhaust gas flowing in the exhaust passage, the exhaust gas heating system can be more effectively used. A further object of the present invention is to provide an apparatus for processing the exhaust gas, which can realize this method.

Solution to Problem

A first aspect of the present invention is provided with a method for processing an exhaust gas introduced to an exhaust emission purifier in a vehicle mounting an internal combustion engine thereon including a bypass valve for opening/closing a bypass passage of the exhaust gas branching from an exhaust passage upstream of an exhaust turbine in an exhaust turbocharger and merging with an exhaust passage positioned between the exhaust turbine and the exhaust emission purifier, a fuel supplying valve for supplying fuel to the exhaust passage upstream of a branch portion between the bypass passage and the exhaust passage, and igniting means for igniting the fuel supplied from the fuel supplying valve in the exhaust passage upstream of the branch portion between the bypass passage and the exhaust passage, comprising a first exhaust gas processing mode for opening the bypass valve, activating the igniting means, and supplying the fuel to the exhaust passage from the fuel supplying valve to ignite the supplied fuel, a second exhaust gas processing mode for closing the bypass valve and supplying the fuel to the exhaust passage from the fuel supplying valve without activating the igniting means, a step for, in a case of igniting the fuel by the igniting means, determining whether or not there is a flame failure (i.e. including flame-loss, flame-out, failure to ignite and ignition failure) of the fuel, and a step for selecting the first exhaust gas processing mode in a case where it is determined that there is not the flame failure of the fuel and selecting the second exhaust gas processing mode in a case where it is determined that there is the flame failure of the fuel.

In the present invention, in a case of an operating status of a vehicle in which a high-temperature burning gas obtained by igniting the fuel with the igniting means does not miss, the first exhaust gas processing mode is selected. In the first exhaust gas processing mode, the high-temperature burning gas is introduced from the bypass passage to the exhaust emission purifier to promote activation thereof. In reverse, in a case of the operating status of the vehicle in which the high-temperature burning gas obtained by igniting the fuel with the igniting means misses, the second exhaust gas processing mode is selected. In the second exhaust gas processing mode, the fuel supplied from the fuel supplying valve is introduced via the exhaust turbine to the exhaust emission purifier in a state of uniformly mixing with the exhaust gas from the internal combustion engine.

In the method for processing the exhaust gas according to the first aspect of the present invention, the step for determining whether or not there is the flame failure of the fuel may comprise a step for detecting an exhaust gas temperature, a step for detecting a flow rate of the exhaust gas flowing into the exhaust emission purifier, and a step for detecting an oxygen concentration in the exhaust gas. In addition, there may be further provided a third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and not supplying the fuel to the exhaust passage from the fuel supplying valve, and a step for selecting the third exhaust gas processing mode in a case where the detected exhaust gas temperature exceeds a predetermined temperature.

The step for determining whether or not there is the flame failure of the fuel may comprise a step for determining whether the vehicle is in the decelerating state or the internal combustion engine is in an idling state. Here, in the case where it is determined that the vehicle is in the decelerating state or the internal combustion engine is in the idling state, it may be determined that there is not the flame failure of the fuel, and in the case where it is determined that neither the vehicle is in the decelerating state nor the internal combustion engine is in the idling state, it may be determined that there is the flame failure of the fuel. In addition, there may be further provided a third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and not supplying the fuel, a step for detecting an exhaust gas temperature, and a step for selecting the third exhaust gas processing mode in the case where the detected exhaust gas temperature exceeds a predetermined temperature.

There may be further provided a step for determining presence/absence of malfunction in an opening/closing action of the bypass valve based upon a variation in an exhaust gas temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode. In addition, the step for determining the presence/absence of the malfunction in the opening/closing action of the bypass valve may determine that the opening/closing action of the bypass valve is wrong in a case the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.

A second aspect of the present invention is provided with an apparatus, in which an exhaust turbocharger and an exhaust emission purifier are incorporated, for processing an exhaust gas introduced from an internal combustion engine to the exhaust emission purifier, comprising a bypass conduit for defining a bypass passage of the exhaust gas branching from an exhaust passage upstream of an exhaust turbine in the exhaust turbocharger and merging with an exhaust passage positioned between the exhaust turbine and the exhaust emission purifier, a bypass valve mounted on the bypass conduit for opening/closing the bypass passage, an actuator for performing an opening/closing action of the bypass valve, a fuel supplying valve for supplying fuel to the exhaust passage upstream of a branch portion between the exhaust passage and the bypass passage, igniting means for igniting the fuel supplied from the fuel supplying valve to the exhaust passage upstream of the branch portion between the exhaust passage and the bypass passage, and control means for controlling each of operations of the actuator, the fuel supplying valve and the igniting means, wherein the control means comprises a flame failure determining unit for determining, in a case where the fuel is ignited by the igniting means, whether or not there is a flame failure of the fuel, and a processing mode selecting unit for selecting a first exhaust gas processing mode for opening the bypass valve, activating the igniting means and supplying the fuel to the exhaust passage from the fuel supplying valve to ignite the fuel or a second exhaust gas processing mode for closing the bypass valve and supplying the fuel to the exhaust passage from the fuel supplying valve without activating the igniting means, based upon the determination result of the flame failure determining unit.

In the present invention, in a case of an operating status of a vehicle in which a high-temperature burning gas obtained by igniting the fuel with the igniting means does not miss, the first exhaust gas processing mode is selected, wherein the high-temperature burning gas is introduced from the bypass passage to the exhaust emission purifier to promote activation thereof. On the contrary, in a case of the operating status of the vehicle in which the high-temperature burning gas obtained by igniting the fuel with the igniting means misses, the second exhaust gas processing mode is selected. In the second exhaust gas processing mode, the fuel supplied from the fuel supplying valve is introduced via the exhaust turbine to the exhaust emission purifier in a state of uniformly mixing with the exhaust gas from the internal combustion engine.

The apparatus for processing the exhaust gas according to the second aspect of the present invention may be further provided with an exhaust gas temperature sensor for detecting a temperature of the exhaust passage, an exhaust gas flow sensor for detecting a flow rate of the exhaust gas flowing into the exhaust emission purifier, and an O₂ sensor for detecting an oxygen concentration in the exhaust gas. In this case, the flame failure determining unit in the control means may determine whether or not a flame failure of the fuel based upon the detected exhaust gas temperature, exhaust gas flow rate and oxygen concentration. In addition, the processing mode selecting unit in the control means may select the third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and not supplying the fuel in a case where the exhaust gas temperature detected by the exhaust gas temperature sensor exceeds a predetermined temperature.

There may be further provided load detecting means for detecting a load of the internal combustion engine, wherein the flame failure determining unit in the control means determines that there is not the flame failure of the fuel in a case where the load detected by the load detecting means is below a light load and there is the flame failure of the fuel in the other case. In addition, there may be further provided an exhaust gas temperature sensor for detecting a temperature of the exhaust passage. Here, the processing mode selecting unit in the control means may select the third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and further not supplying the fuel to the exhaust passage in a case where the exhaust gas temperature detected by the exhaust gas temperature sensor exceeds a predetermined temperature.

The control means may further comprise a failure determining unit for determining presence/absence of malfunction in an opening/closing action of the bypass valve based upon a variation in the exhaust temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode. In addition, the failure determining unit may determine that the opening/closing action of the bypass valve is wrong in a case where the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.

Advantageous Effects of Invention

According to the present invention, a time for warming-up of the exhaust emission purifier at a cold time can be made shorter than conventional, and the supply source of the secondary air becomes unnecessary. In addition, even while the internal combustion engine is operating, it is possible to maintain the active state of the exhaust emission purifier by using the fuel supplying valve and the igniting means.

By selecting the first exhaust gas processing mode in a case where the ignition of the fuel is possible, based upon the exhaust gas temperature, the exhaust gas flow rate and the oxygen concentration, the high-temperature exhaust gas can be efficiently introduced to the exhaust emission purifier without the missing thereof. In addition, by selecting the second exhaust gas processing mode in a case where the continuous combustion of the fuel is impossible, the fuel can be introduced to the exhaust emission purifier in a state of being uniformly dispersed by using the exhaust turbine.

In a case where the detected exhaust gas temperature exceeds the predetermined temperature, the third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and not supplying the fuel to the exhaust passage from the fuel supplying valve is selected, thus making it possible to restrict wasteful consumption of the fuel.

Presence/absence of malfunction in the opening/closing action of the bypass valve maybe determined based upon a variation in the exhaust gas temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode. More specially it may be determined that the opening/closing action of the bypass valve is wrong in a case where the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.

In a case where it is determined that the fuel does not miss when the load of the internal combustion engine is below a light load and there is the flame failure of the fuel in the other case, for example, in a case where the vehicle is in the decelerating state or the internal combustion engine in an idling state, the first exhaust gas processing mode is selected.

Thereby the high-temperature burning gas can be efficiently introduced to the exhaust emission purifier without the missing thereof. In addition, by selecting the second exhaust gas processing mode in a case where neither the vehicle is in the decelerating state nor the internal combustion engine is in the idling state, the fuel can be introduced to the exhaust emission purifier in a state of being uniformly dispersed by using the exhaust turbine.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an outline diagram of an embodiment where the present invention is applied to a compression ignition type internal combustion engine;

FIG. 2 is a control block diagram of a primary portion in the embodiment shown in FIG. 1;

FIG. 3 is a map schematically showing a relation between an intake air quantity, an exhaust gas temperature, an oxygen concentration, and an ignitable region;

FIG. 4 is flowchart showing the control procedure of the embodiment shown in FIG. 1; and

FIG. 5 is a flow chart showing the control procedure of the other embodiment in the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment in which the present invention is applied to a compression ignition type internal combustion engine will be in detail explained with reference to FIG. 1 to FIG. 5. The present invention is not, however, limited to the embodiment, and the construction thereof maybe freely modified corresponding to required characteristics. The present invention is effectively applied to a spark ignition type internal combustion engine in which gasoline, alcohol, LNG (Liquefied Natural Gas) or the like is used as fuel to be ignited by a spark plug, for example.

A primary portion of an engine system in the present embodiment is schematically shown in FIG. 1, and a control block thereof is shown in FIG. 2. It should be noted that in FIG. 1, a valve-operating mechanism for intake and exhaust in an engine 10, a muffler and the like are omitted for convenience.

The engine 10 is a compression ignition type internal combustion engine in which light oil as fuel is directly injected into a combustion chamber 10 a in a compressed state from a fuel injection valve 11 to generate spontaneous ignition of the fuel.

A quantity and injection timing of the fuel supplied into the combustion chamber 10 a from the fuel injection valve 11 are controlled based upon operating status of the vehicle including a depressing travel of an accelerator pedal 12 by a driver by an ECU (Electric Control Unit) 13. The depressing travel of the accelerator pedal 12 is detected by an accelerator opening sensor 14, and the detection information is outputted to the ECU 13.

The ECU 13 includes an operating status determining unit 13 a for determining an operating status of the vehicle based upon information from the accelerator opening sensor 14, various sensors to be described later and the like, a fuel injection quantity setting unit 13 b, and a fuel injection valve driving unit 13 c. The fuel injection quantity setting unit 13 b sets an injection quantity and an injection timing of the fuel from the fuel injection valve 11 based upon the determination result from the operating status determining unit 13 a. The fuel injection valve driving unit 13 c controls an operation of the fuel injection valve 11 in such a manner that the quantity of the fuel set by the fuel injection quantity setting unit 13 b is injected at the set timing from the injection valve 11.

An intake port 15 a and an exhaust port 15 b respectively exposed to the combustion chamber 10 a are formed in a cylinder head 15, which is provided with a valve-operating mechanism (not shown) incorporated therein and including an intake valve 16 a for opening/closing the intake port 15 a and an exhaust valve 16 b for opening/closing the exhaust port 15 b. The aforementioned fuel injection valve 11 is also incorporated in the cylinder head 15.

An intake conduit 17 is connected to the cylinder head 15 in such a manner as to be communicated with the intake port 15 a for defining an intake passage 17 a together with the intake port 15 a. The intake conduit 17 is provided with a throttle valve 19 incorporated therein for adjusting an opening of the intake passage 17 a through a throttle actuator 18. The ECU 13 further includes a throttle opening setting unit 13 d and a throttle valve driving unit 13 e. The throttle opening setting unit 13 d sets an opening of the throttle valve 19 based upon the determination result by the aforementioned operating status determining unit 13 a. The throttle valve driving unit 13 e controls an operation of the throttle actuator 18 such that the throttle valve 19 opens in the degree of opening set by the throttle opening setting unit 13 d.

A cylinder block 20 in which a piston 20 a reciprocates is provided with a crank angle sensor 21 mounted thereon for detecting a rotational phase of a crank shaft 20 c connected through a connecting rod 20 b to the piston 20 a, that is, a crank angle thereof, which is outputted to the ECU 13. The operating status determining unit 13 a in the ECU 13 obtains in real time the rotational phase of the crank shaft 20 c, an engine rotational speed, further, a vehicle speed and the like, based upon information from the crank angle sensor 21.

The engine 10 is provided with an EGR (Exhaust Gas Recirculation) system 23 recirculating a part of the exhaust gas flowing in the exhaust passage 22 a to the intake passage 17 a, an exhaust turbocharger 24, an exhaust emission purifier 25 and an exhaust gas processing apparatus 26, which are incorporated therein.

The EGR system 23 designed to reduce nitrogen oxides in the exhaust gas and improve fuel consumption is provided with an EGR conduit 27 defining an EGR passage 27 a and an EGR valve 28 provided in the EGR conduit 27 for controlling a flow rate of the exhaust gas flowing in the EGR passage 27 a. The EGR conduit 27 has one end communicated with an exhaust conduit 22 defining the exhaust passage 22 a together with the exhaust port 15 b and the other end communicated with the intake passage 17 a between the aforementioned throttle valve 9 and a surge tank 17 b arranged downstream of the throttle valve 19.

In the present embodiment, in a case where the operating status determining unit 13 a in the ECU 13 determines that a vehicle mounting the engine 10 thereon is in a preset EGR performance region, an opening of the EGR valve 28 is set in accordance with an operating status of the vehicle at this time by an EGR rate setting unit 13 f in the ECU 13. An EGR valve driving unit 13 g in the ECU 13 controls the EGR valve 28 to an opening set by the EGR rate setting unit 13 f and in the other case, basically drives the EGR valve 28 to a closing state in such a manner as to stop the EGR passage 27 a.

The exhaust turbocharger (hereinafter, described simply as turbocharger) 24 performs supercharging into the combustion chamber 10 a by using kinetic energy of the exhaust gas flowing in the exhaust passage 22 a to enhance a charging efficiency of intake air. The turbocharger 24 has a primary portion constructed of a compressor 24 a and an exhaust turbine 24 b rotating integrally with the compressor 24 a. The compressor 24 a is incorporated in a portion of the intake conduit 17 positioned upstream of the throttle valve 19. The exhaust turbine 24 b is incorporated in a portion of the exhaust conduit 22 connected to the cylinder head 15 to be communicated with the exhaust port 15 b. It should be noted that, for reducing a temperature of intake air heated through the compressor 24 a by transfer of heat from the exhaust turbine 24 b exposed to the high-temperature exhaust gas, an intercooler 24 c is incorporated in a portion the intake passage 17 a between the compressor 24 a and the throttle valve 19. In addition, the aforementioned EGR conduit 27 has one end connected to the exhaust conduit 22 upstream of the exhaust turbine 24 b.

The exhaust emission purifier 25 for rendering harmful substances generated by combustion of a mixture in the combustion chamber 10 a harmless is incorporated in the exhaust conduit 22 defining the exhaust passage 22 a downstream of the exhaust turbine 24 b in the turbocharger 24. The exhaust emission purifier 25 in the present embodiment includes an oxidation catalytic converter 25 a and a DPF (Diesel Particulate Filter) 25 b in that order from the upstream side of the exhaust passage 22 a, but may further include the other catalytic converter such as a NO_(x) catalyst. The oxidation catalytic converter 25 a oxidizes and dissolves unburned components in the exhaust gas, and the DPF 25 b traps particulate matter contained in the exhaust gas and renders it harmless.

The exhaust gas processing apparatus 26 processes the exhaust gas to be introduced from the engine 10 to the exhaust emission purifier 25 to perform quick activation and holding of an active state of the exhaust emission purifier 25, but is usable also for regeneration processing of the aforementioned DPF 25 b. The exhaust gas processing apparatus 26 in the present embodiment is provided with the fuel supplying valve 29, a glow plug 30, a bypass conduit 31, a bypass valve 32, and a bypass valve actuator 33. Further, for smoothly controlling the exhaust gas processing apparatus 26, the aforementioned ECU 13, an airflow meter 34, first and second exhaust gas temperature sensors 35 and 36, and an O₂ sensor 37 are used.

The airflow meter 34 as an exhaust gas flow sensor of the present invention is mounted on a portion of the intake conduit 17 positioned upstream of the compressor 24 a in the turbocharger 24 to detect a flow rate of intake air flowing in the intake passage 17 a, outputting the detected flow rate to the ECU 13. Instead of the airflow meter 34, an exhaust gas flow sensor having the same construction may be mounted on a portion of the exhaust conduit 22 positioned downstream of a merging portion with the bypass conduit 31 and upstream of the exhaust emission purifier 25. The first exhaust gas temperature sensor 35 detects a temperature T_(1n) within the exhaust passage 22 a downstream of a connecting portion with one end of the EGR conduit 27 and upstream of a mounting position of the fuel supplying valve 29 and outputs the detected temperature to the ECU 13. The second exhaust gas temperature sensor 36 is mounted on a portion of the exhaust conduit 22 positioned downstream of a merging portion with the bypass conduit 31 and upstream of the exhaust emission purifier 25. Accordingly the second exhaust gas temperature sensor 36 detects a temperature T_(2n) of the exhaust gas flowing in the exhaust passage 22 a immediately before flowing into the exhaust emission purifier 25 and outputs the detection information to the ECU 13. Instead of the first exhaust gas temperature sensor 35, a catalyst temperature sensor may be incorporated between the oxidation catalytic converter 25 a and the DPF 25 b in the exhaust emission purifier 25. The O₂ sensor 37 is mounted in a portion of the exhaust conduit 22 positioned downstream of the exhaust emission purifier 25 and detects an oxygen concentration D_(n) in the exhaust passage 22 a, which is outputted to the ECU 13. It should be noted that instead of the O₂ sensor 37, an air-fuel ratio detecting sensor may be used.

The fuel supplying valve 29 supplying fuel for performing activation of the exhaust emission purifier 25 or maintaining an active state thereof is mounted on the exhaust conduit 22 in such a manner as to be exposed to the exhaust passage 22 a downstream of a connecting portion to one end of the EGR conduit 27 and upstream of a branch portion to the bypass conduit 31. The fuel supplying valve 29, in a case where the warming-up of the exhaust emission purifier 25 or the regeneration processing of the DPF 25 b is required, supplies fuel toward the exhaust passage 22 a positioned upstream of a branch portion to the bypass passage 31 a defined by the exhaust passage 22 a and the bypass conduit 31. More specially in a case where a temperature detected by the second exhaust gas temperature sensor 36 to be described later is below a predetermined temperature (hereinafter, described as catalyst active temperature) T_(L), a predetermined quantity of fuel is supplied from the fuel supplying valve 29. Therefore, the ECU 13 includes a fuel supplying valve driving unit 13 h for controlling an operation of the fuel supplying valve 29.

The glow plug 30 as the igniting means in the present invention is connected to an in-vehicle power source (not shown) through a switch (not shown) controlled to be ON/OFF by the ECU 13 to be capable of igniting at least a part of the fuel supplied from the fuel supplying valve 29. A glow pug driving unit 13 i in the ECU 13 changes an activation/deactivation of the glow plug 30 to be ON/OFF.

The ECU 13 includes, in a case where the fuel supplied from the fuel supplying valve 29 to the exhaust passage 22 a is ignited by the glow pug 30, a flame failure determining unit 13 j for determining whether or not the fuel can continue to burn. A map shown in FIG. 3 is stored in the flame failure determining unit 13 j in the present embodiment. The flame failure determining unit 13 j determines whether an operating status of the engine 10 is in an ignitable region of fuel or in an unignitable region thereof and outputs the determination result to a processing mode selecting unit 13 k in the ECU 13. The determination is made based upon detection signals from the airflow meter 34, the second exhaust gas temperature sensor 36, and the O₂ sensor 37. In FIG. 3, a boundary between the ignitable region and the unignitable region in a case where the O₂ concentration is 15% is shown in a solid line to be associated with an intake air quantity and a first exhaust gas temperature. A broken line shows the boundary between the ignitable region and the unignitable region in a case where the O₂ concentration is 20%. That is, the flame failure determining unit 13 j stores therein a plurality of maps for associating the intake air quantity with the first exhaust gas temperature corresponding to the O₂ concentration.

The bypass conduit 31 is arranged to define the bypass passage 31 a connected to the exhaust passage 22 a in a state of bypassing the exhaust turbine 24 b in the turbocharger 24 and have a downstream end communicated with the exhaust passage 22 a downstream of the exhaust turbine 24 b in the turbocharger 24. The bypass conduit 31 has an upstream end which branches from the exhaust conduit 22 to be positioned downstream of a connecting portion between the exhaust conduit 22 and one end of the EGR conduit 27 and upstream of the exhaust turbine 24 b. On the other hand, the downstream end of the bypass conduit 31 merges at a portion of the exhaust conduit 22 defining the exhaust passage 22 a connected through the exhaust turbine 24 b in the turbocharger 24 to the exhaust emission purifier 25.

The bypass valve 32 driven by the bypass valve actuator 33 is mounted on the bypass conduit 31 to open/close the bypass passage 31 a. The bypass valve 32 is constructed of being capable of introducing the burning gas ignited by the glow plug 30 from the bypass passage 31 a to the exhaust emission purifier 25 without via the exhaust turbine 24 b in the opening state. The ECU 13 includes a bypass valve driving unit 131 for controlling an operation of the bypass valve actuator 33.

The fuel supplying valve driving unit 13 h, the glow plug driving unit 13 i, and the bypass valve driving unit 13I respectively drive the fuel supplying valve 29, the glow plug 30, and the bypass valve 32 according to the processing mode selected by the processing mode selecting unit 13 k in the ECU 13.

The processing mode selecting unit 13 k selects the first to third exhaust gas processing modes based upon the determination result by the flame failure determining unit 13 j in the ECU 13. In the first exhaust gas processing mode, the fuel is supplied to the exhaust passage 22 a from the fuel supplying valve 29, the glow plug 30 is activated, and the bypass valve 32 is maintained to be in an opening state. The first exhaust gas processing mode is selected in a case where the vehicle is in an operating status in which when the fuel is ignited, the ignited fuel can be introduced toward the exhaust emission purifier 25 without the missing thereof. In the second exhaust gas processing mode, the fuel is supplied to the exhaust passage 22 a from the fuel supplying valve 29, the glow plug 30 is deactivated, and the bypass valve 32 is maintained to be in a closing state. The second exhaust gas processing mode is selected in a case where the vehicle is in an operating status in which the DPF 25 b is under regenerating state and when the fuel is ignited, there is the flame failure of the fuel. In the third exhaust gas processing mode, the fuel is not supplied to the exhaust passage 22 a from the fuel supplying valve 29, the glow plug 30 is deactivated, and the bypass valve 32 is maintained to be in the closing state. The third exhaust gas processing mode is selected in a case where the vehicle is in an operating status in which the warming-up of the exhaust emission purifier 25 and the regeneration processing of the DPF 25 b are not required.

The ECU 13 includes a failure determining unit 13 m for detecting presence/absence of malfunction in an opening/closing action of the bypass valve 32 and an indicator driving unit 13 n. The failure determining unit 13 m determines, in a case where the first exhaust gas processing mode in the middle of the executing is changed to the second exhaust gas processing mode or the third exhaust gas processing mode, when a variation of an exhaust gas temperature T_(2n) to be detected does not show a reducing inclination based upon information of the exhaust gas temperature from the second exhaust gas temperature sensor 36, that the opening/closing action of the bypass valve 32 is wrong. In the first exhaust gas processing mode, the high-temperature burning gas is in a state of entering into the exhaust emission purifier 25. In a case where this state changes to the second exhaust gas processing mode or the third exhaust gas processing mode, ignition of the fuel by the glow plug 30 is not executed, which is therefore the ground that the temperature T_(2n) of the exhaust gas flowing into the exhaust emission purifier 25 is substantially reduced. The indicator driving unit 13 n serves to inform a driver that the opening operation of the bypass valve 32 is wrong, based upon the determination result of the failure determining unit 13 m. A warning indicator 38 for it is provided in the vehicle compartment (not shown). The warning indicator 38 may be only provided for causing a driver to draw attention aurally or visually.

The ECU 13 is a well-known one chip microprocessor and includes a CPU, a ROM, a RAM, an involatile memory, and an input/output interface which are connected with each other by a data bus, and the like. The ECU 13 executes a predetermined computing processing based upon detection signals of the aforementioned sensors 14, 21, and 35 to 37, the airflow meter 34, and the like in such a manner as to provide a smooth action of the engine 10. In addition, operations of the fuel injection valve 11, the throttle valve 19, the EGR valve 28, the glow plug 30, the fuel supplying valve 29, the bypass valve 32 and the like are controlled according to preset programs.

An intake air supplied into the combustion chamber 10 a from the intake passage 17 a forms a mixture with fuel injected into the combustion chamber 10 a from the fuel injection valve 11. The mixture is usually burned by spontaneous ignition immediately before a compression top dead center of a piston 20 a, and an exhaust gas generated by it is discharged from the exhaust conduit 22 through the exhaust emission purifier 25 to an atmosphere. In this case, unburned components in the exhaust gas are oxidized and dissolved by the oxidation catalytic converter 25 a, and the particulate material is trapped by the DPF 25 b to be purified, which is discharged to an atmosphere.

It should be noted that, when the particulate matter continues to be trapped by the DPF 25 b, since the DPF 25 b is gradually clogged with the particulate matter, it is necessary to eliminate the clogging of the DPF 25 b by burning the particulate matter. The regeneration processing of the DPF 25 b is therefore executed at a DPF regeneration processing unit 13 o in the ECU 13 based upon information of a cumulative fuel injection quantity injected by the fuel injection valve 11, a cumulative operating time of the engine 10, a difference between an exhaust gas pressure upstream of the DPF 25 b and an exhaust gas pressure downstream thereof, and the like. The DPF regeneration processing unit 13 o provides an injection quantity of fuel from the fuel injection valve 11 for regenerating the DPF 25 b, and in addition thereto, in the present embodiment, fuel is supplied into the exhaust passage 22 a also from the fuel supplying valve 29. That is, a supplying operation of the fuel into the exhaust passage 22 a from the fuel supplying valve 29 is basically performed in a case where the exhaust emission purifier 25 is in an inactive state. However, for quickly executing the regeneration processing of the DPF 25 b in the exhaust emission purifier 25, the fuel can be also supplied into the exhaust passage 22 a from the fuel supplying valve 29.

As a result, in addition to the activation of the exhaust emission purifier 25 and the maintenance of the active state thereof, the regeneration processing of the DPF 25 b can be also quickly executed. Particularly the exhaust gas processing apparatus 26 is remarkably advantageous in improving a so-called cold emission state immediate after a cold start of the engine 10. Further, since an ignition position of fuel is at a distance from the fuel supplying valve 29, uniform mixing between the fuel and the exhaust gas is possible, thus making it possible to more largely reduce incomplete combustion of the fuel than the conventional exhaust gas heating system.

An operational procedure of the exhaust gas processing apparatus 26 in the present embodiment will be explained with reference to a flow chart in FIG. 4. First, at a step of S11, it is determined whether or not an exhaust gas temperature T_(2n) detected by the second exhaust gas temperature sensor 36 is below a catalyst active temperature T_(L). Here, when it is determined that the exhaust gas temperature T_(2n) is below the catalyst active temperature T_(L), that is, it is necessary to heat the exhaust emission purifier 25 for activation or maintain an active state thereof, the process goes to a step of S12. At this step of S12, a first exhaust gas temperature T_(1n), an intake air flow rate Q_(n), and an oxygen concentration D_(n) in the exhaust gas respectively are detected by the first exhaust gas temperature sensor 35, the airflow meter 34, and the O₂ sensor 37. In addition, at a step of S13, the flame failure determining unit 13 j determines whether or not a current operating status of the engine 10 is in an ignitable region of fuel based upon the detection information. Here, in a case where it is determined that the current operating status of the engine 10 is in the ignitable region, that is, the current operating status is an atmosphere where a high-temperature burning gas can continue to be generated by igniting the fuel supplied to the exhaust passage 22 a by the glow plug 30, the process goes to a step of S14. At this step of S14, the first exhaust gas processing mode, in which the bypass valve 32 is in an opening state, the glow plug 30 is changed to an ON-state as a power supplying state and the fuel from the fuel supplying valve 29 is supplied to the exhaust passage 22 a, is executed. In consequence, the burning gas which has become high in temperature due to ignition of the fuel is introduced from the bypass passage 31 a to the exhaust emission purifier 25. That is, since the high-temperature burning gas bypasses the exhaust turbine 24 b as a flow resistance, the heat of the high-temperature burning gas is not absorbed by the exhaust turbine 24 b, and the exhaust emission purifier 25 is efficiently heated.

Subsequent to the step of S14, at a step of S15, a flag showing that the bypass valve 32 is opened is set, and steps after the first step of S11 are repeated.

In a case where at the aforementioned step of S13, it is determined that the current operating status of the vehicle is not in the ignitable region, that is the current operating status is an atmosphere where even when the fuel supplied to the exhaust passage 22 a is ignited by the glow plug 30, there is the flame failure of the fuel, the process goes to a step of S16. At this step of S16, it is determined whether or not the DPF 25 b is in the regeneration processing. Here, in a case where it is determined that the DPF 25 b is in the regeneration processing, that is, it is determined that, although the fuel can not be ignited, it is effective to supply the fuel to the exhaust emission purifier 25 for the regeneration processing of the DPF 25 b, the process goes to a step of S17. At this step of S17, the second exhaust gas processing mode, in which the bypass valve 32 is in a closing state, the glow plug 30 is changed to an OFF-state as a non-power supplying state, and the fuel from the fuel supplying valve 29 is supplied to the exhaust passage 22 a, is executed. In consequence, the fuel supplied to the exhaust passage 22 a is introduced through the exhaust turbine 24 b to the exhaust emission purifier 25. In this case, since dispersion of the fuel into the exhaust gas is promoted by a stirring effect of the exhaust turbine 24 b, the reforming and the thermal decomposition of the fuel by the oxidation catalytic converter 25 a in the exhaust emission purifier 25 is promoted. Thereby the high-temperature exhaust gas burned in the oxidation catalytic converter 25 a is introduced to the DPF 25 b, thus making it possible to efficiently perform the regeneration thereof.

Subsequent to the step of S17, at a step of S18 it is determined whether or not a flag is set. Here, in a case where it is determined that the flag is set, that is, the bypass valve 32 is changed from the opening state to the closing state, the process goes to a step S19. At this step of S19, the failure determining unit 13 m determines a variation of the exhaust gas temperature T_(2n) detected by the second exhaust gas temperature sensor 36, that is, whether or not the detected exhaust gas temperature T_(2n) is below the previously detected exhaust gas temperature T_(2 (n−1)). Here, in a case where it is determined that the exhaust gas temperature T_(2n) is below the previously detected exhaust gas temperature T_(2 (n−1)), that is, a reduction of the exhaust gas temperature T_(2n) is generated since the ignition of the fuel by the glow plug 30 is not performed, it is determined that there is no malfunction in the opening/closing action of the bypass valve 32, and the process goes to a step of S20. At this step of S20, the flag is reset, and steps after S11 are again repeated. In addition, in a case where it is determined that the flag is not set, that is, the bypass valve 32 is not changed from the opening state to the closing state, steps after S11 are again repeated.

On the other hand, in a case where it is determined at the step of S16 that the DPF 25 b is not during the regeneration processing, that is, there is a possibility of imposing an adverse effect on the exhaust emission purifier 25 by supplying fuel, the process goes to a step of S21. Also in a case where at the step of S11, it is determined that the exhaust gas temperature T_(2n) is higher than the catalyst active temperature T_(L), that is, it is not necessary to heat the exhaust emission purifier 25 since the exhaust emission purifier 25 is in an active state, the process goes to the step of S21. At this step of S21, the third exhaust gas processing mode for stopping an operation of the exhaust gas processing apparatus 26 is executed. That is, the bypass valve 32 is closed, the power supply to the glow plug 30 changes into an OFF-state, and supply of the fuel from the injection supplying valve 29 is stopped. Thereafter, the process goes to the step of S18, wherein it is determined whether or not a flag showing that the bypass valve 32 is opened is set.

In a case where at the step of S19, it is determined that the exhaust gas temperature T_(2n) is equal to or higher than the previously detected exhaust gas temperature T_(2 (n−1)), that is, it is determined that there is malfunction in the glow plug 30, the bypass valve 32 or the bypass valve actuator 33, the process goes to a step of S22. At the step of S22, the indicator driving unit 13 n drives the warning indicator 38 to inform a passenger of the malfunction of the exhaust gas processing apparatus 26, and outputs a failure warning for promoting the repair and resets the flag, thus completing the control in regard to the exhaust gas processing.

In the aforementioned embodiment, it is determined whether or not the fuel is ignitable based upon the first exhaust gas temperature T_(2n), the intake air flow rate Q_(n), and the O₂ concentration D_(n), but it is possible also to determine whether or not the fuel is ignitable based upon a load of the engine 10. More specially in a case where the load of the engine 10 is below a light load, for example, a vehicle is in the decelerating state or the engine 10 is in an idling state, it can be determined that there is no possibility that there is the flame failure of the ignited fuel since a flow speed of the exhaust gas flowing in the exhaust passage 22 a is slow. In reverse, in a case where the load of the engine 10 is in a state other than the above, it can be determined that there is a possibility that there is the flame failure of the ignited fuel since the flow speed of the exhaust gas flowing in the exhaust passage 22 a is rapid. In this case, the load detection of the engine 10 can be calculated by the operating status determining unit 13 a in the ECU 13. More specially the load of the engine 10 can be calculated based upon a depressing travel of the accelerator pedal 12 detected by the accelerator opening sensor 14 and an engine rotation speed calculated based upon the detection information from the crank angle sensor 21. That is, the ECU 13 includes load detecting means in the present invention.

A control flow in the other embodiment of the present invention is shown in FIG. 5, but steps having the same functions as the above embodiment are referred to as identical codes, and the identical explanation is omitted. In the present embodiment, at the step of S11, when it is determined that the exhaust gas temperature T_(2n) is below the catalyst active temperature T_(L), that is, it is necessary to heat the exhaust emission purifier 25 for activation or maintain an active state thereof, the process goes to a step of S23. Further, it is determined whether or not the vehicle is in the decelerating state. In a case where it is determined that the vehicle is in the decelerating state, that is, the accelerator pedal 12 is not depressed and an engine rotational speed is reduced or a negative acceleration is generated, the process goes to the step of S14. As a result, the first exhaust gas processing mode is executed. In addition, in a case where at the step of S23 it is determined that the vehicle is not in the decelerating state, the process goes to a step of S24, wherein it is determined whether or not the engine 10 is in an idling state. Here, in a case where it is determined that the engine 10 is in the idling state, that is, the accelerator pedal 12 is not depressed and the engine rotational speed is in an idling rotational region, the process goes to the step of S14, wherein the first exhaust gas processing mode is executed.

In a case where at the step of S24 it is determined that the engine 10 is not in the idling state, that is, the load of the engine is not below a light load, the process goes to the step of S16, wherein it is determined whether or not the DPF 25 b is during regeneration processing, and thereafter the same procedure as that of the above embodiment is executed.

It should be noted that, the present invention should be interpreted based only upon the matters described in claims, and in the aforementioned embodiments, all changes and modifications included within the spirit of the present invention can be made other than the described matters. That is, all the matters in the described embodiments are made not to limit the present invention, but can be arbitrarily changed according to the application, the object and the like, including every construction having no direct relation to the present invention.

Reference Signs List

-   10 ENGINE -   10 a COMBUSTION CHAMBER -   11 FUEL INJECTION VALVE -   12 ACCELERATOR PEDAL -   13 ECU -   13 a OPERATING STATUS DETERMINING UNIT -   13 b FUEL INJCETION SETTING UNIT -   13 c FUEL INJECTION VALVE DRIVING UNIT -   13 d THROTTLE OPENING SETTING UNIT -   13 e THROTTLE VALVE DRIVING UNIT -   13 f EGR RATE SETTING UNIT -   13 g EGR VALVE DRIVING UNIT -   13 h FUEL SUPPLYING VALVE DRIVING UNIT -   13 i GLOW PLUG DRIVING UNIT -   13 j FLAME FILURE DETERMINING UNIT -   13 k PROCESSING MODE SELECTING UNIT -   13 l BYPASS VALVE DRIVING UNIT -   13 m FAILURE DETERMINING UNIT -   13 n INDICATOR DRIVING UNIT -   13 o DPF REGENERATION PROCESSING UNIT -   14 ACCELERATOR OPENING SENSOR -   15 CYLINDER HEAD -   15 a INTAKE PORT -   15 b EXHAUST PORT -   16 a INTAKE VALVE -   16 b EXHAUST VALVE -   17 INTAKE CONDUIT -   17 a INTAKE PASSAGE -   17 b SURGE TANK -   18 THROTTLE ACTUATOR -   19 THROTTLE VALVE -   20 CYLINDER BLOCK -   20 a PISTON -   20 b CONNECTING ROD -   20 c CRANK SHAFT -   21 CRANK ANGLE SENSOR -   22 EXHAUST CONDUIT -   22 a EXHAUST PASSAGE -   23 EGR SYSTEM -   24 EXHAUST TURBOCHARGER -   24 a COMPRESSOR -   24 b EXHAUST TURBINE -   24 c INTERCOOLER -   25 EXHAUST EMISSION PURIFIER -   25 a OXIDATION CATALYTIC CONVERTER -   25 b DPF -   26 EXHAUST GAS PROCESSING APPARATUS -   27 EGR CONDUIT -   27 a EGR PASSAGE -   28 EGR VALVE -   29 FUEL SUPPLYING VALVE -   30 GLOW PLUG -   31 BYPASS CONDUIT -   31 a BYPASS PASSAGE -   32 BYPASS VALVE -   33 BYPASS VALVE ACTUATOR -   34 AIRFLOW METER -   35 FIRST EXHAUST GAS TEMPERATURE SENSOR -   36 SECOND EXHAUST GAS TEMPERATURE SENSOR -   37 O₂ SENSOR -   38 WARNING INDICATOR 

1-14. (canceled)
 15. A method for processing an exhaust gas introduced to an exhaust emission purifier in a vehicle mounting an internal combustion engine thereon including a bypass valve for opening/closing a bypass passage of the exhaust gas branching from an exhaust passage upstream of an exhaust turbine in an exhaust turbocharger and merging with an exhaust passage positioned between the exhaust turbine and the exhaust emission purifier, a fuel supplying valve for supplying fuel to the exhaust passage upstream of a branch portion between the bypass passage and the exhaust passage, and igniting means for igniting the fuel supplied from the fuel supplying valve in the exhaust passage upstream of the branch portion between the bypass passage and the exhaust passage, comprising: a first exhaust gas processing mode for opening the bypass valve, activating the igniting means, and supplying the fuel to the exhaust passage from the fuel supplying valve to ignite the supplied fuel; a second exhaust gas processing mode for closing the bypass valve and supplying the fuel to the exhaust passage from the fuel supplying valve without activating the igniting means; a step for determining whether or not there is a flame failure of the fuel when the fuel is ignited by the igniting means; and a step for selecting the first exhaust gas processing mode in a case where it is determined that there is not the flame failure of the fuel, and selecting the second exhaust gas processing mode in a case where it is determined that there is the flame failure of the fuel.
 16. A method for processing an exhaust gas according to claim 15, wherein the step for determining whether or not there is the flame failure of the fuel comprises: a step for detecting an exhaust gas temperature; a step for detecting a flow rate of the exhaust gas flowing into the exhaust emission purifier; and a step for detecting an oxygen concentration in the exhaust gas.
 17. A method for processing an exhaust gas according to claim 16, further comprising: a third exhaust gas processing mode for closing the bypass valve, not activating the igniting means, and not supplying the fuel to the exhaust passage from the fuel supplying valve; and a step for selecting the third exhaust gas processing mode in a case where the detected exhaust gas temperature exceeds a predetermined temperature.
 18. A method for processing an exhaust gas according to claim 15, wherein the step for determining whether or not there is a flame failure of the fuel comprises: a step for determining whether the vehicle is in the decelerating state or the internal combustion engine is in an idling state, wherein in a case where it is determined that the vehicle is in the decelerating state or the internal combustion engine is in the idling state, it is determined that there is not the flame failure of the fuel, and in a case where it is determined that neither the vehicle is in the decelerating state nor the internal combustion engine is in the idling state, it is determined that there is the flame failure of the fuel.
 19. A method for processing an exhaust gas according to claim 18, further comprising: a third exhaust gas processing mode for closing the bypass valve, not activating the igniting means, and not supplying the fuel to the exhaust passage from the fuel supplying valve; a step for detecting an exhaust gas temperature; and a step for selecting the third exhaust gas processing mode in a case where the detected exhaust gas temperature exceeds a predetermined temperature.
 20. A method for processing an exhaust gas according to claim 17, further comprising: a step for determining presence/absence of malfunction in an opening/closing action of the bypass valve based upon a variation in the exhaust gas temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 21. A method for processing an exhaust gas according to claim 20, wherein the step for determining the presence/absence of the malfunction in the opening/closing action of the bypass valve determines that the opening/closing action of the bypass valve is wrong in a case where the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 22. A method for processing an exhaust gas according to claim 19, further comprising: a step for determining presence/absence of malfunction in an opening/closing action of the bypass valve based upon a variation in the exhaust gas temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 23. A method for processing an exhaust gas according to claim 22, wherein the step for determining the presence/absence of the malfunction in the opening/closing action of the bypass valve determines that the opening/closing action of the bypass valve is wrong in a case where the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 24. An apparatus, in which an exhaust turbocharger and an exhaust emission purifier are incorporated, for processing an exhaust gas introduced from an internal combustion engine to the exhaust emission purifier, comprising: a bypass conduit for defining a bypass passage of the exhaust gas branching from an exhaust passage upstream of an exhaust turbine in the exhaust turbocharger and merging with an exhaust passage positioned between the exhaust turbine and the exhaust emission purifier; a bypass valve mounted on the bypass conduit for opening/closing the bypass passage; an actuator for performing an opening/closing action of the bypass valve; a fuel supplying valve for supplying fuel to the exhaust passage upstream of a branch portion between the exhaust passage and the bypass passage; igniting means for igniting the fuel supplied from the fuel supplying valve to the exhaust passage upstream of the branch portion between the exhaust passage the bypass passage; and control means for controlling each of operations of the actuator, the fuel supplying valve and the igniting means, wherein the control means comprises: a flame failure determining unit for determining whether or not there is a flame failure of the fuel, in a case where the fuel is ignited by the igniting means; and a processing mode selecting unit for selecting a first exhaust gas processing mode for opening the bypass valve, activating the igniting means and supplying the fuel to the exhaust passage from the fuel supplying valve to ignite the fuel, or a second exhaust gas processing mode for closing the bypass valve and supplying the fuel to the exhaust passage from the fuel supplying valve without activating the igniting means, based upon the determination result of the flame failure determining unit.
 25. An apparatus for processing an exhaust gas according to claim 24, further comprising: an exhaust gas temperature sensor for detecting a temperature of the exhaust passage; an exhaust gas flow sensor for detecting a flow rate of the exhaust gas flowing into the exhaust emission purifier; and an O₂ sensor for detecting an oxygen concentration in the exhaust gas, wherein the flame failure determining unit in the control means determines whether or not there is the flame failure of the fuel based upon the detected exhaust gas temperature, exhaust gas flow rate and oxygen concentration.
 26. An apparatus for processing an exhaust gas according to claim 25, wherein the processing mode selecting unit in the control means selects the third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and not supplying the fuel to the exhaust passage from the fuel supplying valve in a case where the exhaust gas temperature detected by the exhaust gas temperature sensor exceeds a predetermined temperature.
 27. An apparatus for processing an exhaust gas according to claim 24, further comprising: load detecting means for detecting a load of the internal combustion engine, wherein the flame failure determining unit in the control means determines that there is not the flame failure of the fuel in a case where the load detected by the load detecting means is below a light load and there is the flame failure of the fuel in the other case.
 28. An apparatus for processing an exhaust gas according to claim 27, further comprising: an exhaust gas temperature sensor for detecting a temperature of the exhaust passage, wherein the processing mode selecting unit in the control means selects the third exhaust gas processing mode for closing the bypass valve, not activating the igniting means and not supplying the fuel to the exhaust passage from the fuel supplying valve in a case where the exhaust gas temperature detected by the exhaust gas temperature sensor exceeds a predetermined temperature.
 29. An apparatus for processing an exhaust gas according to claim 26, wherein the control means further comprises: a failure determining unit for determining presence/absence of malfunction in an opening/closing action of the bypass valve based upon a variation in the exhaust temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 30. An apparatus for processing an exhaust gas according to claim 29, wherein the failure determining unit determines that the opening/closing action of the bypass valve is wrong in a case the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 31. An apparatus for processing an exhaust gas according to claim 28, wherein the control means further comprises: a failure determining unit for determining presence/absence of malfunction in an opening/closing action of the bypass valve based upon a variation in the exhaust temperature in a case where the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode.
 32. An apparatus for processing an exhaust gas according to claim 31, wherein the failure determining unit determines that the opening/closing action of the bypass valve is wrong in a case the exhaust gas temperature is not lowered at the time the first exhaust gas processing mode is changed to the second or third exhaust gas processing mode. 